We measured black carbon (BC) with a seven-wavelength aethalometer (AE-31) at the Nam Co Lake (NCL), the hinterland of the Tibetan Plateau (TP) from May 2015 to April 2016. The daily average concentration of BC was 145 +/- 85 ng m(-3), increasing by 50% since 2006. The seasonal variation of BC shows higher concentrations in spring and summer and lower concentrations in autumn and winter, dominated by the adjacent sources and meteorological conditions. The diurnal variation of BC showed that its concentrations peaked at 9:00-16:00 (UTC + 8), significantly related to local human activities (e.g., animal-manure burning and nearby traffic due to the tourism industry). The concentration-weighted trajectory (CWT) analysis showed that the long-distance transport of BC from South Asia could also be a potential contributor to BC at the NCL, as well as the biomass burning by the surrounding residents. The analyses of the absorption coefficient and absorption angstrom ngstrom exponent show the consistency of sourcing the BC at the NCL. We suggest here that urgent measures should be taken to protect the atmospheric environment at the NCL, considering the fast-increasing concentrations of BC as an indicator of fuel combustion.

Air pollutants can be transported to the pristine regions such as the Tibetan Plateau, by monsoon and stratospheric intrusion. The Tibetan Plateau region has limited local anthropogenic emissions, while this region is influenced strongly by transport of heavy emissions mainly from South Asia. We conducted a comprehensive study on various air pollutants (PM2.5, total gaseous mercury, and surface ozone) at Nam Co Station in the inland Tibetan Plateau. Monthly mean PM2.5 concentration at Nam Co peaked in April before monsoon season, and decreased during the whole monsoon season (June-September). Monthly mean total gaseous mercury concentrations at Nam Co peaked in July and were in high levels during monsoon season. The Indian summer monsoon acted as a facilitator for transporting gaseous pollutants (total gaseous mercury) but a suppressor for particulate pollutants (PM2.5) during the monsoon season. Different from both PM2.5 and total gaseous mercury variabilities, surface ozone concentrations at Nam Co are primarily attributed to stratospheric intrusion of ozone and peaked in May. The effects of the Indian summer monsoon and stratospheric intrusion on air pollutants in the inland Tibetan Plateau are complex and require further studies. (C) 2021 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.

Water-soluble organic carbon (WSOC) is an important component of carbonaceous aerosols. Increasing evidences show that WSOC absorbs and scatters sunlight in the atmosphere, which is one of the key components of climate change. Despite numbers of related studies, understanding of basic characteristics of WSOC is limited at remote region, such as the Himalayas and Tibetan Plateau (HTP), one of the remotest regions in the world with weak local anthropogenic activities. In this study, we conducted a year-round investigation of multiple aerosol species at Nam Co, a pristine station in inner part of the HTP. The results showed that the annual mean concentrations of PM2.5 and its WSOC were 8.9 +/- 5.4 mu gm(-3) and 249 +/- 111 ng m(-3), respectively, which was among the lowest values in the HTP, representing a clean environment. WSOC of PM2.5 and total suspended particle (TSP) samples were mainly derived from combustion emissions and fine particle of local surface soil, respectively, indicating significant contribution of local sources of the HTP to TSP samples. Similarly, due to the influence of surface soil, respective absorption per mass of WSOC at 365 nm (alpha/pWSOC) of TSP (1.74 +/- 0.94 m(2) g(-1)) was significantly higher than that of PM2.5 (1.22 +/- 0.43 m(2) g(-1)). Seasonally, high and low WSOC concentrations and alpha/pWSOC values appeared at non-monsoon and monsoon periods, respectively. This study provides observational constraints for related researches such as modelling of the environmental impact of WSOC in the HTP.